In recent years, dry eye patients have been increased with spread use of contact lenses and increase in use of VDT. Dry eye is a disease exhibiting symptoms such as xerophthalmia, corneal afflux, foreign body feeling, itching feeling and the like, which results in corneal disorders, in principal, due to a lowered lacrimal secretion. In addition, it is said that when dry eye becomes severe, it also causes paropsia and asthenopia.
It is believed that some causes of lowered lacrimal secretion, there are Riley-day syndrome, Shy-Drager syndrome, Sjögren's syndrome, sarcoidosis, amyloidosis, sequela of radiotherapy, lagophthalmos, vitamin A deficiency, Stevens-Johnson syndrome, occular pemphigoid, blepharitis marginal, meibomitis, sequela of intraoccular surgery, contact lens disorder, diabetic ectocorneal disease, VDT-operation, driving over a long period of time and the like.
The lacrimal fluid exists in a border portion where an eyeball contacts with air, and constitutes a thin fluid layer having a thickness of approximately 7 μm which covers an outermost layer of the eyeball. The lacrimal fluid has a three-layered structure, which consists of, from an outer side, an oily layer, an aqueous layer and a mucinous layer, and each layer plays an important role in preventing the eyeball from dryness. The aqueous layer, which occupies most of the lacrimal fluid thickness, is prevented from the decrement by existing between the oily layer and the mucinous layer to maintain the wettability of the eyeball. The oily layer is in principle secreted from a gland existing around an eyelid, which is called meibom gland, and prevents moisture from evaporation by covering throughout the aqueous layer. Accordingly, when the production of the oily layer is reduced due to meibomitis, the aqueous layer becomes apt to evaporate and, thereby, symptom of dry eye is exhibited. The mucinous layer covers a hydrophobic ectocorneal surface to change the surface to hydrophilic and, thereby, has the function of retaining the aqueous layer on an ectocorneal surface.
The lacrimal fluid has various functions in addition to prevention of dry eye. Other functions of the lacrimal fluid include, for example, protection of cornea and conjunctiva, bacteriostatic action, prevention of infection with bacteria, fungus, virus and the like, feeding of oxygen and a variety of nutritions to cornea and removal of a carbon dioxide gas and metabolites therefrom, dilution and removal of harmful stimuli in the case where cornea and conjunctiva injured, transportation of liquid components such as epidermal growth factors which participate in wound healing and the like and hematocyte components such as fibronectin and the like to the injured portion, retainment of cornea and a conjunctival epithelial cell, regulation of wound healing and the like.
At present, various artificial lacrimal fluid-type eye drops have been sold for the purpose of treatment of lowered lacrimal secretion. However, many of them are a preparations comprising inorganic salts and/or metal chelating agents for the purpose of supplementing the lacrimal fluid and, therefore, although they are temporarily effective in solving the dry feeling of eye followed by a lowered lacrimal secretion, the effect is not sustained because they do not affect the lacrimal secretion itself. In addition, it is difficult to persistently remove unpleasantnesses such as foreign body feeling and itching upon wearing the contact lens, or the burning feeling of eye and the like due to dry eye. Furthermore, when those having a lowered amount of oily secretion from meibom gland increase frequency of treatment with eye drops, the dry feeling of the eye becomes stronger due to washing out of the oily and mucinous layers. This attributes to the problem due to a lacrimal fluid components supplementing therapy, but not a lacrimal secretion promoting therapy, which increases lacrimal secretion itself.
Although there is, as the known lacrimal secretion promoting therapy, a method, in which muscarinic drug such as pilocarpine is used as a lacrimal secretion stimulating agent, it has not been a satisfactory preparation yet because of the problems of side effects and the like. Therefore, ophthalmologists and dry eye patients could do nothing but take the lacrimal fluid supplementing therapy while they knew the therapy has only temporal effects.
As stated above, the ophthalmologists and dry eye patients have desired development of a composition for promoting lacrimal secretion which can be used safely and effectively in the lacrimal secretion promoting therapy, not in the conventional lacrimal fluid components supplementing therapy.
On the other hand, it has been known that PAR (Protease-activated receptor) belongs to a G-protein coupled seven transmembrane receptor family and is a receptor which is activated by a protease. (Hollenberg, M. D., Trends Pharmacol. Sci., 17, 3-6, 1996; Hollenberg, M. D., Trends Pharmacol. Sci., 20, 271-273, 1999). PAR is cleaved at a particular N-terminal site of an extracellular domain by a protease to expose a new N-terminal. It is believed that the newly exposed N-terminal becomes a linear ligand and binds to a known active site to activate the receptor (Hollenberg, M. D., Trends Pharmacol. Sci., 17, 3-6, 1996; Hollenberg, M. D., Trends Pharmacol. Sci., 20, 271-273, 1999; Vu, T. K. et al., Cell, 64, 1057-68, 1991).
It has been reported that there are 4 subtypes, PAR-1, PAR-2, PAR-3 and PAR-4 in PAR and that they have different functions from each other. It has been found that PAR-1, PAR-3 and PAR-4 are activated by thrombin (Vu, T. K. et al., Cell, 64, 1057-1063, 1991; Hollenberg, M. D., Trends Pharmacol. Sci., 17, 3-6, 1996; Ishihara, H. et al., Nature, 386, 502-6, 1997; Kahn, M. L. et al., Nature, 394, 690-4, 1998; Xu, W. F. et al., Proc. Natl. Acad. Sci. USA, 95, 6642-6, 1998), and PAR-2 is activated by trypsin (Nystedt, S. et al., Proc. Natl. Acad. Sci. USA, 91, 9208-12, 1994; Molino, M. et al., J. Biol. Chem., 272, 6011-7, 1997) and tryptase (Molino, M. et al., J. Biol. Chem., 272, 6011-7, 1997; Fox, M. T. et al., FEBS Lett., 417, 267-9, 1997).
A site to be cleaved on the amino acid sequences of PAR-1 (Vu, T. K. et al., Cell, 64, 1057-1063, 1991), PAR-2 (Nystedt, S. et al., Proc. Natl. Acad. Sci. USA, 91, 9208-12, 1994), PAR-3 (Ishihara, H. et al., Nature, 386, 502-6, 1997) and PAR-4 (Kahn, M. L. et al., Nature, 394, 690-4, 1998; Xu, W. F. et al., Proc. Natl. Acad. Sci. USA, 95, 6642-6, 1998) has been known, and it has been also known that PAR-1, PAR-2 and PAR-4 are activated by an exogenous treatment with a synthetic peptide comprising 5-6 amino acids which are synthesized based on an active amino acid sequence at the site to be cleaved (Vu, T. K. et al., Cell, 64, 1057-68, 1991; Nystedt, S. et al., Proc. Natl. Acad. Sci. USA, 91, 9208-12, 1994; Ishihara, H. et al., Nature, 386, 502-6, 1997; Kahn, M. L. et al., Nature, 394, 690-4, 1998; Xu, W. F. et al., Proc. Natl. Acad. Sci. USA, 95, 6642-6, 1998; Dery, O. et al., Am. J. Physiol., 274, C1429-52, 1998).
Activation of inositol 1,4,5-trisphosphate (IP3) and protein kinase C series has been known as one of intracellular signals through PAR-2 (Hollenberg, M. D., Trends Pharmacol. Sci., 20, 271-273, 1999; Dery, O. et al., Am. J. Physiol., 274, C1429-52, 1998; Zheng, X. L. et al., J. Pharmacol. Exp. Ther., 285, 325-34, 1998).
For PAR-2, an inflammatory response (Cirono, G. et al., J. Exp. Med., 183, 821-827, 1996; Kawabata, A. et al., Br. J. Pharmacol., 125, 419-422, 1998), and a constricting and relaxing action in gastric blood vessel and trachea have been reported (Saifeddine, M. et al., Br. J. Pharmacol., 118, 521-531, 1996; Moffatt, J. D. et al., Br. J. Pharmacol., 125, 591-594, 1998; Cocks, T. M. et al., Nature, 398, 156-160, 1999; Hollenberg, M. D. et al., Can. J. Physiol. Pharmacol., 75, 832-884, 1997). In addition, it has been reported that PAR-2 is expressed in prostate, small intestine, colon, liver, kidney and pancreas (Stephan, K. B. et al., Biochem. J., 341, 1009-1016, 1996). However, PAR-2 relating to the lacrimal secretion has not been reported yet, and the present inventors have first demonstrated that a component which activates PAR-2 (that is, an agonist) possesses the lacrimal secretion promoting action.